We investigated the ABA content of Hypogymnia physodes and Peltigera praetextata sampled at natural habitats at different times of a year. The ABA content showed high variability in both lichen species and was far higher in H. physodes than in P. praetextata at ever)' time by a mean factor of about 20. Conjugation of 14C-ABA was only small in wet thalli as well as in desiccating thalli, and no oxidative degradation could be found. Efflux experiments showed relative high rate constants for ABA exchange across tonoplast and plasmalemma. So, conjugation of ABA seems to be supplemented by excretion as regulating mechanisms underlying the observed decreases in ABA content